1. Field of the Invention
This invention relates to a two-pack type coating composition for golf ball excellent in surface durability and to a golf ball using the same.
2. Description of Related Art
The surface layer of a golf ball has a double layer structure in which the lower layer portion is composed of a white enamel coating composition and the upper layer portion is composed of a clear coating composition. The role of this clear coating composition is to protect the ball body and retain its gloss and beautiful appearance.
This kind of coating composition is required to have such excellent impact resistance that the coating withstands the repeated hitting with a golf club and such excellent sand abrasion resistance that the coating with-stands the bunker shot, and also have excellent resistance to contamination with grass sap, excellent weather resistance and excellent water resistance.
Many coating compositions for a golf ball satisfying these properties are now two-pack type polyurethane coating compositions which are cured using a non-yellowing type isocyanate curing agent and a hydroxyl group-containing polyester resin obtained by reacting a polyhydric aliphatic alcohol with a polybasic aliphatic or aromatic acid.
In the case of the golf ball coated with the above-mentioned conventional polyurethane coating composition, the fracture strength of the clear layer of the surface coating film is not great and the elongation thereof is not sufficient, so that face mark flaw, craze, crack and the like tend to be caused by the hitting with a golf club. Moreover, the sand abrasion during the bunker shot and the contamination with grass sap during the shots in the fairway, the rough and the like are violent, so that the gloss and beautiful appearance of a golf ball are liable to be lost. In other words, the clear layer of the conventional polyurethane surface coating film lacks such a durability that the appearance and beautiful sight of a golf ball are retained.
The present inventors have fund that when a compound having an alicyclic structure in the molecule is substituted for at least a part of at least the polyhydric alcohol component in the hydroxyl group-containing polyester which is the main constituent of the above-mentioned polyurethane coating composition, the golf ball coated with the resulting polyurethane coating composition has a durability even when the conventional white enamel coating of the lower layer part is omitted, whereby the above-mentioned problems can be solved and the coating step can be shortened. By this finding, this invention has been completed.